In U.S. Pat. No. 4,818,480 issued Apr. 4, 1989, there is disclosed and claimed a method of making a cathode from a mixture of tungsten and iridium powders using a barium peroxide containing material as the impregnant. Such a material can be barium peroxide alone or a mixture of barium peroxide with iridium or a mixture of barium peroxide with osmium, or a mixture of barium peroxide with rhodium. Though cathodes made by the method of U.S. Pat. No. 4,818,480 deliver adequate energy densities, it would be desirable to provide cathodes which deliver even higher energy densities.